1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method and apparatus for controlling a random access process efficiently in a mobile communication system supporting carrier aggregation.
2. Description of the Related Art
Mobile communication systems provide subscribers and users of the mobile communication systems with voice communication services while on the move. With the advancement of mobile communication technologies, mobile communications have evolved to support high speed data communication services as well as the voice communication services. Recently, as one of the next generation mobile communication systems, Long Term Evolution (LTE) is a system being standardized by the 3rd Generation Partnership Project (3GPP). LTE systems provide high speed packet-based communication of up to 100 Mbps and are now being commercially deployed.
Unlike the standard voice services, data services are allocated resources according to an amount of data to be transmitted and a channel condition for the transmission. Accordingly, in a wireless communication system, such as cellular communication system, it is important to manage resource allocation based on a resource scheduled for data transmission, a channel condition, and an amount of data to be transmitted. This resource management is important in LTE systems as well, and a scheduler located at an enhanced Node B (eNB) of the LTE system manages and assigns radio resources. Recent research and development is focused on the LTE-Advanced (LTE-A) system for improving a data transmission rate with the adaptation of several new techniques to a legacy LTE system.
Carrier Aggregation is one of these new techniques. Unlike a typical communication system using an uplink as a signal carrier in uplink and downlink transmissions between a User Equipment (UE) and an eNB, carrier aggregation makes it possible to combine a primary carrier and at least one secondary carrier in order to increase a transmission/reception data transmission rate in proportion to a number of aggregated carriers. In an LTE-A system, a cell operating on the primary carrier is referred to as a primary cell (or may also be referred to as a PCell or a first cell), and a cell operating on a secondary carrier is referred to as a secondary cell (or may also be referred to as an SCell or second cell).
Meanwhile, in a case where locations of antennas responsible for radio communication on the primary and secondary carriers are determined in consideration of the introduction of a repeater and/or a Remote Radio Head (RRH) (e.g., a transmit/receive antenna operating on the primary carrier may be located at a position of the eNB while an antenna operating on the secondary carrier is located at the position of the RRH), uplink timings are configured for the receive antennas near and far from the UE differently according to a location of the UE. Accordingly, when a plurality of uplink timings are configured in the communication system, there is a need of a method for controlling the random access procedure in order to acquire a plurality of uplink timings efficiently. Accordingly, there is a need for a method for handling a problem and/or failure of a random access procedure efficiently so as to acquire multiple uplink timings configured in the mobile communication system.